Process for assembling electrodes



y 12, 1954/ e. A. FREEMAN 3,132,409

PROCESS FOR ASSEMBLING ELECTRODES Filed Dec. 22, 1959 FIG. 3.

INVENTOR 26 650/?65 ,9. FEEEMHN ATTORNEY 'be locked together by means ofa force fit. -'since the inner coil must be tightly fitted onto as topermit the outer coil to be threaded over the inner coil and lockedtherewith without displacing the latter, it frequently happened that theexpanded medial section United States Patent 3,132,409 PROCESS FORASSEMBLING ELECTRODES 7 George A. Freeman, East Orange, N.J., assignorto Westinghouse Electric Corporation, corporation of Pennsylvania FiledDec. 22, 1959, Ser. No. 861,339 Claims. (Cl. 2925.14)

East Pittsburgh, Pa., 21

improved thermionic electrode for high pressure mercury vapor (HPMV)lamps that markedly increases both the useful life and lumen maintenanceof such lamps by providing a reservoir of electron-emissive materialthat is shielded from the gaseous discharge and the erosive effectthereof. This is accomplished by depositing the emission material bymeans of a dip process between the spaced intermediate turn or turns ofa refractory wire coil that has closed end sections and is mounted on asuitable core member such as a tungsten rod. A tightly Wound outer coilis then threaded over and interlocked with the inner coil. This enclosesthe expanded medial section of the inner coil and the reservoir ofemission material therein. The emission material is thus pro-'tectedfrom the arc and the sputtering of such material onto thebulb'surface and resultant of the bulb is markedly reduced. -To avoidtime-consuming and costly integrating operations such as welding or thelike the inner coil and core member are preferably dimensioned so thatthey can However, the rod so progressive blackening of the inner coilpartially collapsed and became permanently distorted as the rod wasbeing inserted. When this occurred the inner coil had to be discardedsince the spacing between turns of the expanded section was decreasedand this section thus could not hold or accommodate the required amountof emission material. Narrowing the diameter tolerances of the rod andinner coil as much as practical to minimize the compressive stress onthe inner coil and the tendency of the medial section to collapse duringassembly failed to solve this problem.

It is accordingly the general object of the present invention toovercome the foregoing and other problems associated with the assemblyand use of composite thermionic electrodes of the aforesaid character.

Another and more specific object is the provision of a method which willenable the core rod and inner coil component of such an electrode to beassembled with a minimum amount of labor and shrinkage and which can bereadily adapted to automatic assembly techniques.

The aforesaid objects of the invention, and others which will becomeapparent as the description proceeds, are achieved by holding the innercoil to prevent it from turning or being displaced in an axialdirection, but without constricting it or obstructing access to itsinterior, and

then concurrently rotating the core rod and inserting it into the coilwhile the latter is so held. Rotation of the rod during its insertioncauses the coil to relax or open up, so to speak, and thus permit thenecessary force to be exerted on the rod without causing the expandedmedial section of the coil to collapse or become distorted, especiallyif the rod is rotated at a predetermined rate of speed and in apredetermined direction with respect to the direction in which the coilwas wound.

A better understanding of the invention and the manner "ployed inassembling various kinds of devices wherein one in which theaforementioned objectives are attained can he had by referring to theaccompanying drawing, wherein:

FIG. 1 is a side elevational view on a reduced scale of an arc tube foran HPMV lamp which incorporates thermionic electrodes assembled inaccordance with this invention;

FIG. 2 is an enlarged side elevational view, partly broken away and insection, of one of the electrodes of the arc tube shown in FIG. 1;

FIG. 3 is an end view of the arc-supporting portion of the electrodeillustrated in FIG. 2;

FIGS. 4 and 5 are side elevational views of the inner coil before andafter the coil legs have been trimmed, respectively;

FIG. 6 is a side elevational view of an alternative coil embodiment;

FIG. 7 is a holder;

FIG. 8 is a cross-sectional View of the holder taken along the lineVIIIVIII of FIG. 7, in the direction of the arrows;

FIG. 9 is a plan view of the coil holder corresponding to the view shownin FIG. 7 but with the coil illustrated in FIG. 5 inserted into theholder and locked in keyed relation therewith;

FIG. 10 is a cross-sectional view of the holder and inserted coil takenalong the line XX of FIG. 9, in the direction of the arrows; and

FIG. 11 is a side-sectional view of the coil and holder plan view of apreferred form of coil the coil preparatory to the Withdrawal of therod-and-coil assembly from the holder.

While the present invention can be advantageously emmember isforce-fitted into another member that is susceptible to distortion whencompressively stressed, it has particular utility in connection with theassembly of thermionic electrodes for HPMV lamps and has accordinglybeen so illustrated and will be so described.

With specific reference to the form of the invention shown in thedrawing, in FIG. 1 there is shown an arc tube :12 for an HPMV lampcomprising a tubular envelope 14 of quartz or the like that is closed'ateach end by a press seal 16. A pair of oppositely disposed thermionicelectrodes 20 are anchored in each of the seals 16 and electricallyconnect with the usual ribbon-conductor assemblies 18 which arehermetically embedded in and extend through the aforesaid seals. Afilling of ionizable starting gas such as argon or the like is alsosealed within the envelope 14 along with a charge of mercury 13 and anauxiliary electrode 21 that is disposed adjacent one of the mainelectrodes 20 and electrically connects with "a separateribbon-conductor assembly 19.

As shown more particularly in FIGS. 2 and 3, each of the main electrodes20 consist generally of an outer coil 24 and an inner coil 26 of linearconfiguration, and a 'core member such as a cylindrical tungsten rod 22that is inserted into and locked by means of a force fit with the innercoil. Both the outer coil 24 and the inner coil 26 are of substantiallyuniform diameter and are wound from refractory metal wire such astungsten for example. 65.

The outer coil 24 is tightly wound so as to form a closed helix and isthreaded over and interlocked with the inner coil 26 the end turnswhereof are also tightly wound and constitute closed end sections. Theintermediate turns 28 of the inner coil 26 are spaced a predetermineddistance from'each other and from the adjacent end turns and constitutean expanded medial section that is filled with a predetermined amount ofsuitable electron-emissive material 30 such as the well-known alkalineearth carbonates, thoria, etc., or mixtures thereof. The emissionmaterial 30 is preferably applied by mixing it with a suitable binder toform a slurry and dipping the rod-audinner coil assembly therein. Uponhardening the emission material firmly adheres to and bridges theintermediate turns 28 as shown. The end of the rod 22 opposite theaforesaid coils is preferably shaped to provide a flat end section 21 inorder to facilitate the electrical connection thereof with theribbon-conductor assembly 18 and its subsequent embedment in the pressseal 16. The aforesaid inner and outer coils are preferably located apredetermined distance inward from the cylindrical end of the core rod22 as shown.

The present invention relates to an improved method for assemblingcomposite type electrodes of the aforesaid character rather than to suchelectrodes per se and this method will now be described.

Since the method can be most conveniently practiced with a specific typeof inner coil component, two examples of such components will first bedescribed. In FIG. 4 there is shown one design wherein the inner coil 26as wound has a leg 31 at each end which protrude at right angles fromthe same side of the coil. Instead of cutting both legs 31 in adirection parallel to the longitudinal axis of the coil as heretofore toprovide a so-called square cut end turn 32 such as that shown in FIG. 5,only one leg is thus processed and the other severed at a point locateda predetermined distance from the coil body. Thus, at least one of theend turns of the inner coil 26 is terminated by a substantially straightend segment 34 that protrudes laterally from the outer surface of thecoil body and constitutes a tangential extension of the aforesaid endturn, as illustrated in FIGS. 2, 3 and 5. To facilitate anchoring theend segment 34 in the manner hereinafter described, said segmentprojects beyond the outer surface of the coil a distance at leastequivalent to the diameter of the wire from which the inner coil iswound and preferably about twice the wire diameter. This permits the leg31 at that end of the coil to be cut while the coil is still on thecoiling machine thus affording the additional advantages of reducing thecost of the coil by eliminating at least one of the manual cuttingoperations heretofore required and the resultant burr at the entrance tothe coil that necessitated, in turn, a deburring operation and themaintenance of close diameter tolerances to permit easy insertion of therod 22.

Alternatively, instead of employing a cutting wheel to form the squarecut end turn 32 the coil leg 31 can be cut in a direction normal to thelongitudinal axis of the coil to provide another type of inner coil 26awhich has an end turn 32a that is tapered rather than terminatedabruptly, as shown in FIG. 6. This type coil is preferred since bothends of the coil can then be trimmed by machine instead of manually asheretofore thereby further reducing the manufacturing cost of the coil.

Assembly of the core rod 22 with the inner coil 26 is accomplished inaccordance with this invention by concurrently rotating and insertingthe rod into the coil while the latter is held in such a manner thatdisplacement thereof in both an axial and radial direction is prevented,without obstructing the entrance of or access to the in terior of thecoil along a path coincident with the longitudinal axis thereof. Apreferred apparatus for holding the inner coil 26 during the assemblythereof with the rod 22 in accordance with the foregoing procedure isillustrated in FIGS. 7 and 8. As there shown, the holder comprises arigid support member 36 having a major cavity 38 that extends inwardlyfrom one end of said member and merges with a minor cavity 40 that opensinto and coaxially extends from the bottom of said major cavity. Both ofthe aforesaid cavities are of cylindrical configuration, the majorcavity being at least as long as but slightly larger in diameter thanthe outside diameter of the inner coil 26, as for example .010 of aninch in the case of a 1000 watt coil that has an outside diameter ofapproximately .149 of an inch. The minor cavity 40 is slightly largerthan the diameter of the rod 22 and has a length equal to the distancebetween the cylindrical end of the rod 22 and the outermost turn 32 ofthe inner coil 26 when the latter is locked in its position of use onsaid rod.

Due to the difference in diameter of the aforesaid major and minorcavities there is provided an inwardly protruding annular shoulder 41 atthe bottom of the major cavity 38 which is adapted by virtue of itslocation to serve as a stop for the inner coil 26 when the latter isplaced into the holder as set forth below. A recess such as a groove 39is provided in the face of the support member 36 which groovecommunicates with and extends tangentially from the major cavity 33, asshown most particularly in FIG. 7. The depth of the groove 39 is atleast equivalent to the diameter of the wire from which the inner coil26 is wound and is of sufficient length to accommodate the uncoiled endsegment 34. The minor cavity 40 may be vented to the atmosphere as by apassageway 42 that extends from the bottom thereof to the proximate faceof the support member 36.

To assemble the rod 22 with the inner coil 26 the end of the coilopposite the end with the uncoiled end segment 34 is inserted into thesupport member 36 and the coil oriented so that the aforesaid endsegment falls into the groove 39. The inner coil 26 is thus locked orkeyed with the support member 26 and prevented from turning and isseated against and supported by the annular shoulder 41 at the bottom ofthe major cavity 38, as shown in FIGS. 9 and 10. The core rod 22 is thenconcurrently rotated about its own axis and inserted into the inner coil26 along a path coincident with the longitudinal axis thereof, the rodpreferably being rotated in a direction opposite to the direction ofrotation defined by the turns at the entrance end of the coil (asillustrated in FIG. 11). This causes the coil to open up or relax, so tospeak, and be temporarily enlarged thus permitting the rod to beinserted without compressively distorting the intermediate turns 28 ofthe coil. It has been found that the rod 22 can be inserted with aminimum of thrust when it is rotated at approximately 60 rpm. or lessand for this reason speeds in this order of magnitude are preferred.However, the speed of rotation is not critical and can be variedconsiderably.

The axial thrust on the rod 22 is continued until the cylindrical endthereof seats against the bottom 43 of the minor cavity 40 and the innercoil 26 thus precisely located in its position of use on the rod.Rotation of the rod is then stopped and the rod-and-coil assemblywithdrawn from the support member 36 and the subsequent opera tionsrequired to complete the fabrication of the electrode 20 are carriedout.

It has been found that by assembling the rod 22 and inner coil 26 in theforegoing manner the shrinkage due to distorted coils during rodinsertion surprisingly dropped from about 25% and higher to less than2%.

It will be apparent that the inner coil 26 can be prevented from turningwithin the holder by means other than the above-mentioned combination ofan interlocking groove 39 and uncoiled end segment 34. For example, theend of the square cut end turn 32 could be engaged and the coil thusprevented from turning by means of a suitable stop that projects eitherfrom the annular shoulder 41 or the side wall of the major cavity 38, inwhich case the aforesaid uncoiled end segment or groove would not berequired.

It will be recognized from the foregoing that the objects of theinvention have been achieved by providing an improved method ofassembling the rod and coil components of a composite thermionicelectrode, which method not only reduces the manufacturing cost of thecoil but can be readily adapted to automatic manufacturing techniques.

While one embodiment of the invention has been i1- lustrated anddescribed, it is to be understood that various modifications can be madetherein without departing from the spirit and scope of this invention.

I claim:

1. In the manufacture of a composite electrode comprising a refractorywire coil of linear configuration and a core member having an endportion that is larger in cross-section than the inside diameter of saidcoil by an amount sufficient to enable the coil to be locked in assembled relationship on said core member solely by means of a force fit,the method of assembling said Wire coil and core member withoutpermanently distorting the coil and changing the spacing between theturns thereof comprising;

holding one end of the coil at a location such that the coil is heldstationary and its interior is accessible along a path coincident withthe longitudinal axis of the coil,

rotating the core member about its longitudinal axis,

inserting the end portion of said rotating core member into theaforesaid end of said coil along said path to temporarily enlarge theportion of said coil engaged by said core member and thereby enable thelatter to freely enter the coil,

continuing the concurrent rotation and insertion of said core memberuntil said coil is located in its assembled position on said coremember, and then discontinuing the rotation and axial movement of saidcore member to permit the temporarily enlarged portion of said coil toreturn to its original size and thus compressively grip the core member.

2. The method of assembling a refractory wire coil and a core member asset forth in claim 1 wherein the coil is so oriented with respect to therotating core member that the turns of said coil beginning at theentrance end thereof define a direction of rotation that is opposite tothe direction in which the core member is being rotated.

3. In the manufacture of a composite electrode comprising a refractoryWire coil of linear configuration having an end turn that is terminatedby an uncoiled end segment which protrudes laterally beyond the body ofsaid coil, and a support rod having a cylindrical end portion that islarger in diameter than the inside diameter of said coil by an amountsuificient to enable the coil to be locked in assembled relationship onsaid rod solely by means of a force fit, said coil having at least oneintermediate turn that is spaced a predetermined distance from theadjacent turns and constitutes an expanded medial section that isadapted to hold a predetermined amount of emission material and tends tocollapse and become shorter when said coil is compressed in an axialdirection, the method of assembling said coil and rod withoutsubstantially permanently distorting or altering the length of saidexpanded medial section, which method comprises;

engaging the laterally protruding end segment of said coil turn toprevent the coil from turning and moving in an axial direction withoutrendering its interior inaccessible along a path substantiallycoincident with the longitudinal axis of the coil, rotating the supportrod about its longitudinal axis at a predetermined rate of speed and ina direction opposite to the direction of rotation defined by the turnsof said coil beginning at said laterally protruding end segment,inserting the cylindrical end portion of said rotating rod into saidcoil along the aforesaid path to temporarily enlarge the portion of saidcoil engaged by said rod'and enable the latter to be freely insertedtherein,

continuing the concurrent rotation and insertion of said rod until thecylindrical end portion thereof extends through said coil and the latteris disposed in assembled relationship with said rod, and thendiscontinuing the rotation and axial movement of said rod to permit thetemporarily enlarged portion of said coil to return to its original sizeand thus compressively grip the rod.

4. The method of assembling the refractory wire coil and support rodcomponents of a composite electrode as set forth in claim 3 wherein thefree end of said coil is seated against and supported by an aperturedstop mem ber during the assembly operation.

5. The method of assembling the refractory Wire coil and support rodcomponents of a composite electrode as set forth in claim 3 wherein saidrod is rotated at a speed of approximately r.p.m.

References Cited in the file of this patent UNITED STATES PATENTS969,256 Durie Sept. 6, 1910 1,870,968 Sinden Aug. 9, 1932 2,210,061Caminez Aug. 6, 1940 2,225,853 Baker Dec. 24, 1940 2,619,706 Vause Dec.2, 1952 2,765,420 Martt Oct. 2, 1956 2,820,920 Penon Jan. 21, 19582,900,184 Lauring Aug. 18, 1959 2,919,485 Gabor Jan. 5, 1960

1. IN THE MANUFACTURE OF A COMPOSITE ELECTRODE COMPRISING A REFRACTORY WIRE COIL OF LINEAR CONFIGURATION AND A CORE MEMBER HAVING AN END PORTION THAT IS LARGER IN CROSS-SECTION THAN THE INSIDE DIAMETER OF SAID COIL BY AN AMOUNT SUFFICIENT TO ENABLE THE COIL TO BE LOCKED IN ASSEMBLED RELATIONSHIP ON SAID CORE MEMBER SOLELY BY MEANS OF A FORCE FIT, THE METHOD OF ASSEMBLING SAID WIRE COIL AND CORE MEMBER WITHOUT PERMANENTLY DISTORTING THE COIL AND CHANGING THE SPACING BETWEEN THE TURNS THEREOF COMPRISING; HOLDING ONE END OF THE COIL AT A LOCATION SUCH THAT THE COIL IS HELD STATIONARY AND ITS INTERIOR IS ACCESSIBLE ALONG A PATH COINCIDENT WITH THE LONGITUDINAL AXIS OF THE COIL, ROTATING THE CORE MEMBER ABOUT ITS LONGITUDINAL AXIS, INSERTING THE END PORTION OF SAID ROTATING CORE MEMBER INTO THE AFORESAID END OF SAID ALONG SAID PATH TO TEMPORARILY ENLARGE THE PORTION OF SAID COIL ENGAGED BY SAID CORE MEMBER AND THEREBY ENABLE THE LATTER TO FREELY ENTER THE COIL, CONTINUING THE CONCURRENT ROTATION AND INSERTION OF SAID CORE MEMBER UNTIL SAID COIL IS LOCATED IN ITS ASSEMBLED POSITION ON SAID CORE MEMBER, AND THEN DISCONTINUING THE ROTATION AND AXIAL MOVEMENT OF SAID CORE MEMBER TO PERMIT THE TEMPORARILY ENLARGED PORTION OF SAID COIL TO RETURN TO ITS ORIGINAL SIZE AND THUS COMPRESSIVELY GRIP THE CORE MEMBER. 